1. Field of the Invention
The present invention relates to a method for recovering a semiconductor polishing slurry (hereinafter, often called as “polishing slurry”) which would be used in a polishing step in a manufacturing process of semiconductor, and particularly to a method for recovering a used semiconductor polishing slurry with active elements such as abrasives and (an) additive(s) which are dissolved in the dispersion medium of the used slurry, whereby the abrasives and the additive(s) can be recovered with no additional addition of the abrasives, the additive agent(s) for repeating the polishing step.
The manufacturing process of semiconductor includes the steps of forming a base material such as a wafer and a glass directed at a liquid crystal substrate and a mask, forming a manufacturing apparatus member, and manufacturing a device such as an element or a pattern through the processing of the base material and the like.
2. Background of the Invention
Recently, with the development of speedup of a personal computer, it is required for semiconductor integrated circuits (“IC”s) to be employed for the personal computer to be integrated in higher density. In order to comply with the requirement of the higher density integration of the ICs, the wiring patterns must be miniaturized while a multilayered structure must be employed.
In the employment of the multilayered structure, it is required that the surface roughness for the wafer as a base and each layer of the multilayered structure is reduced than ever so that the deterioration of the step coverage at steps and the fluctuation in coating thickness of a photoresist can be reduced.
In this point of view, the surface of the wafer as the base and the surface of each layer of the multilayered structure are polished by using a polishing slurry in order to remove the surface unevenness of each layer thereof.
In the formation of contact holes and via holes by means of CVD (chemical vapor deposition) using tungsten and the formation of a damascene structure by embedding the wiring trenches with Cu wirings, the thus obtained tungsten film and the thus obtained Cu film are polished by using the polishing slurry until the surface levels of the tungsten film and the Cu film become almost equal to the surface level of an insulating film formed around the hole areas and the damascene structure area while the tungsten film and the Cu film are left at the hole areas and the damascene structure area.
In the polishing step in the semiconductor manufacturing process, the surface of the wafer attached to a spindle is contacted with a polishing pad provided on a rotation table with supplying the polishing slurry to the contact area between the wafer and the polishing pad while driving the rotation table.
As the polishing slurry used in the semiconductor manufacturing process, such a polishing slurry as having a composition of polishing member as fumed silica and an ultrapure water, as occasion demands, with an additive element as an iron salt and an organic component, the polishing member and the additive element being dispersed in the ultrapure water.
In the case where such a polishing slurry as having a composition as described above is employed in the semiconductor polishing step, the polishing slurry contains a specific kind of metallic ion commensurate with the composition of the substance to be polished and is fed in a container. After the polishing step is completed, the polishing slurry and the polishing scraps remaining on the polishing pad are washed with the ultrapure water and then, fed in the container.
In Reference 1, the excess water of the used polishing slurry contained in the container is removed via a filter so that the concentration of the used polishing slurry is controlled. Then, the ions are removed from the used polishing slurry via an ion-exchange resin or the like, and the short components are compensated in reference to the composition of the original polishing slurry, and large particles such as polishing scraps are removed via a particle-size controlling filter. In this way, the used polishing slurry is recovered.    [Reference 1] JP-A 11-010540 (KOKAI)    [Reference 2] JP-A 9-314466 (KOKAI)
By the way, since the used polishing slurry contained in the container includes a large amount of washing water as described above, first of all, the excess water must be removed from the used polishing slurry in the recovering process thereof. In this case, an additive such as a stabilizer, a catalyst, a pH controlling component and the like, which are water-soluble and contained in the original polishing slurry, are removed with the excess water, so that the polishing slurry is wasted and another treatment may be required when one or more of the components removed with the excess water are regulated in disposal. In the latter case, it costs to conduct the additional treatment.